Conventionally, technology has been proposed that, in a case of there being a wheel speed difference in either of between the front/rear wheels or between left/right wheels of an electric four-wheel drive vehicle, determines as excessive slip of wheels occurring exceeding the permissible limit, and performs switching from an independent one side wheel drive state (2WD) to an both side wheel (all-wheel) drive state (AWD) (for example, refer to Patent Document 1). In addition, with Patent Document 1, in a case of being a state in which there is wheel speed difference during vehicle stop, takeoff is performed in AWD upon subsequent takeoff.
According to Patent Document 1, AWD is performed only in a case of a wheel speed difference occurring in either of between left/right and front/rear wheels, and having determined as being necessary to perform AWD. AWD is thereby stopped in a case of there being no AWD necessity, even if the driver designates AWD. For this reason, it has been said to be able suppress useless wear on the motor brushes, as well as able to prolong the motor life and improve fuel consumption and electrical cost (hereinafter referred to as “driving efficiency”).
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2007-137307